The diamond miner has also sold its other recent find, a 12.8 carat diamond recovered earlier this month, for US$76,000, or $6,000 per carat, to an undisclosed buyer, it said.
The sale price was "well above the company's $50,000 base-line estimate", London broker, SP Angel, noted.
"The recovery of more, larger diamonds so soon after the 12.8ct stone indicates the [Kareevlei] mine is in a higher-value phase," the broker said.
The average engagement ring weight in the UK is 0.6 carats.
BlueRock's average selling price plummeted to about $290 per carat in 2020, which is at the bottom end of its guidance and blamed on the reduced incidence of larger stones at its flagship project, and the impact of COVID-19.
The news comes after a rocky year for the global diamond industry, which faced the twin perils of supply chain interruptions due to the COVID-19 lockdown and depressed demand for precious gems.
BlueRock Diamonds executive chairman Mike Houston said he was "hopeful" the recent discoveries marked the start of a return to mining higher quality diamonds at Kareevlei.
Recent diamond sorts indicated an increased incidence of diamonds of 3 carats, which was also a significant driver of prices, he said.
"We expect prices to recover in 2021 to reflect this change."
Management plans to double the mining and throughput rate at the mine, in the Northern Cape province of South Africa, in 2021 which ranks among the top 10 globally for average value per carat.
Shares in BlueRock Diamonds have more than halved in the past year, and are currently trading at 47.5p, valuing the company at £4.3 million.